444 INTRODUCTION TO NATURALIST’S CALENDAR. 
migratory period, and are, probably, supplied both from abroad 
and from the more exposed districts of this country. Many of the 
hawks disappear altogether during spring and summer, seeking the 
wilder and more unfrequented grounds to breed and rear their 
young. They reappear again in their usual haunts about the 
middle or end of September. Along our shores and sea marshes 
vast numbers of the plovers, sandpipers, curlews, &c., spend the 
winter, many of which have merely returned with their young from 
a more inland breeding resort. The numerous congregations of 
the young, in autumn, assembling in large flocks together, show 
another kind of migration, being very marked in the black and 
white wagtail, chaffinch, titmice, lapwing, and other plovers, &c. 
A few species, again, which spend the whole season of incubation 
in other parts, are seen once or twice yearly for a short period only. 
The short-eared owl, which in some parts of England is met with 
regularly about the commencement of the winter migratory period, 
is in great part only on return from the more northern parts of this 
country, where it is known to breed. The ring-ousel breeds in the 
alpine districts of England and Scotland, but it is only seen upon 
the English downs, and so often recorded by White, and among 
the mountain ash and cottage gardens in Scotland only for a few 
days, in going and returning to and from their breeding quarters. So 
it is with the common dotterel upon our lower moors, and large 
numbers of our sandpipers, &c., are also only seen for a day or 
two, in similar circumstances. 
The periodical change of colour in the plumage of birds is often 
very marked; it is incidental in great measure to the season of 
incubation, previous to which it gradually approaches completion ; 
and, as that important time arrives, it, along with the voice, obtains 
its fullest vigour, clearness and brilliancy, and the Jatter sometimes 
puts on changes of great contrast with the full and usually chaste 
winter garb. These changes are most characteristic and distinct 
in the waders, water fowl, and gallinaceous birds, and among these 
are almost general ; in other families, although a greater brilliancy 
always occurs, it is only in some that the changes are very marked. 
In some species these changes take piace by a loss of some parts 
of a feather, thereby bringing into view some other portion, and 
so producing a different tint; in others, the colour of the feather 
entirely changes. These variations take place more or less rapidly 
with the seasons ; but in some instances, the change is effected in 
a day or two, as in many of the plovers and sandpipers, some 
